Is there a difference between controlling VPD in a greenhouse grow op compared to a warehouse grow op?

Yes, but this is true of any environment. How you control your VPD is based on a lot of factors, including:

Heat sources

Number of plants in the room

Environmental controls

Air conditioners

Humidifiers

Ventilation

Climate and time of year

Most indoor growers typically use big, powerful AC units to control heat. Air conditioners act as dehumidifiers, so indoor growers need to worry about how to reintroduce moisture into the room.

The humidity in greenhouses is generally elevated at most times of the year. The trick is that the humidity can vary wildly based on the climate. You need extra hardware to compensate for seasonal changes.

What techniques would complement VPD control?

Your basic techniques need to be dialed in before you try VPD control:

Keep the environment as clean as possible. Higher humidity increases the likelihood of pathogenesis.

Be diligent about airflow. Precise VPD control requires optimized air flow.

Monitor your water usage. Be careful to not cut off oxygen to the roots.

When everything else is accounted for, the primary technique that complements VPD control is carbon dioxide injection. Fine-tuned VPD controls the behavior of the stomata, allowing increased gas exchange.

Can you use VPD Control in different life stages?

When you put clones under a dome, you’re keeping the RH high and VPD low. This reduces stress and gives the cuttings time to form roots. Additionally, most growers keep their vegetative humidity higher to reduce stress.

You want to keep your VPD relatively high (low RH) during the flowering cycle. Start with a moderate VPD during the first weeks of flowering, then increase your VPD (lower your RH) towards the end of flowering to prevent pathogenesis.

What are the limitations of VPD control?

The biggest drawback to running a low VPD (high RH) is that you can experience pathogenesis if your rooms aren’t clean. Along the same lines, room homogenization is a struggle. There are always microenvironments forming due to the nature of living organisms.

How do you scale VPD control effectively?

A big mistake people make when they scale up is failing to segment their new space into smaller rooms. Good growing is about having a series of smaller rooms that are easier to control.

How does VPD control affect different cultivars?

There’s not a lot of research out there. All strains can be affected differently in the same environment. Lineages from humid environments will likely prefer humid conditions, and the converse is also probably true.

What would an ideal setup look like to you? What kind of equipment should be integrated?

Humidifiers for starters. Personally, I think that ultrasonic humidifiers work best.

Double or triple redundancy on your air filtration if you’re making an environment hospitable for fungal pathogens.

A controller that integrates your different systems and has multiple setpoints based on factors like time of day.

Some sort of CO2 injection system.

Grow tents are perfect for experimenting because they have a more manageable environment.